In a UMTS (Universal Mobile Telecommunications System) network, for the purposes of improving spectral efficiency and improving the data rates, system features based on W-CDMA (Wideband Code Division Multiple Access) are maximized by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access). For this UMTS network, for the purposes of further increasing high-speed data rates, providing low delay and so on, long-term evolution (LTE) has been under study (see, for example, non-patent literature 1).
In the third-generation mobile communication system, it is possible to achieve a transmission rate of maximum approximately 2 Mbps on the downlink by using a fixed band of approximately 5 MHz. Meanwhile, in a system of the LTE scheme, it is possible to achieve a transmission rate of about maximum 300 Mbps on the downlink and about 75 Mbps on the uplink by using a variable band which ranges from 1.4 MHz to 20 MHz. Furthermore, in the UMTS network, for the purpose of achieving further broadbandization and higher speed, successor systems of LTE have been under study (for example, LTE-Advanced (LTE-A)). For example, in LTE-A, there is a plan to expand the 20-MHz maximum system band of LTE specification to approximately 100 MHz.
In a system of the LTE scheme (LTE system), there is a proposal to adopt hybrid ARQ (HARQ), which uses error correction (FEC: Forward Error Correction) and retransmission control (ARQ: Automatic Repeat reQuest) in combination (see, for example, non-patent literature 1). In this HARQ, it is possible to effectively cope with, for example, random errors on the mobile terminal apparatus UE side due to noise, by requesting retransmission of received data with an error, from the mobile terminal apparatus UE.
In particular, in the LTE system, there is a proposal to adopt HARQ, which involves soft combining. This HARQ to involve soft combining is a technique to achieve received data of high reliability by storing received data with an error in a buffer memory for retransmission control (to be more specific, an LLR (Log Likelihood Ratio) storage buffer memory) and combining this data with data that is retransmitted later (retransmission data).